It is known that crystalline polyarylene sulfides have high heat resistance. However, the maximum utilization of such property in combination with other materials can not be made as yet. This is because a suitable adhesive capable of bonding molded articles of crystalline polyarylene sulfides is not found as yet. In other words, crystalline polyarylene sulfides have resistance to solvents, and hence an appropriate solvent which can sufficiently dissolve crystalline polyarylene sulfides have not been found.
In this connection, .alpha.-chloronaphthalene is known as a solvent capable of dissolving the crystalline polyarylene sulfides when the crystalline polyarylene sulfides are polyphenylene sulfides. However, the smell thereof is not proper for industrial uses. Further, N-methylpyrrolidone can dissolve phenylene sulfide oligomers, but can not dissolve phenylene sulfide polymers.
When the polyarylene sulfides are non-crystalline copolymers comprising an m-dihalobenzene and a p-dihalobenzene, tetrahydrofuran and chloroform are known as solvents [see, JP-B-52-12239 (the term "JP-B" as used herein means an "examined Japanese patent publication")]. However, the heat resistance is poor because the copolymers are non-crystalline.
Further, concentrated sulfuric acid is known as a solvent when the polyarylene sulfides are polyphenylene sulfide ketones. However, it is the present condition that it is industrially difficult to remove the concentrated sulfuric acid. Furthermore, a mixed solvent of 1,2,4-trichlorobenzene and p-cholorophenol is known. However, there are problems with regard to smell and toxicity.
Accordingly, there has been proposed a method wherein a polyarylene sulfide is dispersed in a dispersion medium, the dispersion medium is then removed and the polyarylene sulfide is heated to a temperature of not lower than the crystalline melting point of the polyarylene sulfide. However, a film having a uniform thickness can not be obtained, and moreover a thin film can not be obtained by this method.